chamando metodo

class PostsController < ApplicationController
  before_filter :authenticate_user!
  before_filter :load_post_and_project, except: :create
  
  def publish
    @post.publish!
    
    default_respond_to
  end
  
  def mark_as_spam
    @post.spam!
    
    default_respond_to
  end
  
  private
  def load_post_and_project
    @post = current_user.administrable_posts.find(params[:id])
    @project = @post.project
  end
  
  def default_respond_to
    respond_to do |format|
      format.html { redirect_to project_path(@project) }
      format.js
    end
  end
end

Usando respond_with

class PostsController < ApplicationController
  before_filter :authenticate_user!
  before_filter :load_post_and_project, except: :create
  respond_to :html, :js
  
  def create
    @post = current_user.posts.new(params[:post])
    @post.save
    @project = @post.project
    if @project.user == current_user
      @post.approve!
      @post.ancestors.map { |ancestor| ancestor.approve! unless ancestor.approved? }
    end

    respond_with(@project)
  end
  
  def publish
    @post.publish!
    
    respond_with(@project)
  end
  
  def mark_as_spam
    @post.spam!
    
    respond_with(@project)
  end
  
  private
  def load_post_and_project
    @post = current_user.administrable_posts.find(params[:id])
    @project = @post.project
  end
end